Treating manganese electroplating solutions



Patented June 13, 1950 TREATING MANGANESE ELEGTROPLATING' SOLUTIONS .lohn Koster, Washington, D. C, assignor to Crimora Research & Development Corporation,- Crimora, Va., a corporation of Virginia No Drawing.

2 Claims.

Application February 13, 1946, Serial N0. 647,320 7 This invention relates to the production of electrolytic manganese of high purity and at high current efiiciency. It relates especially to the control of the sulfur content of electrolytic manganese. An aim of this invention is to provide methods of treating manganese solutions for electrolysis which will provide for the deposition of electrolytic manganese substantially in the alpha or brittle form at high current efiiciencies over long plating periods.

Other aims and advantages of the invention will appear in the following specification describing the preferred method of practicing the same.

In the known art, electrolytic manganese is usually plated from solutions containing manganese and ammonium salts to which has been added a sulfur-containing addition agent. This sulfur-containing agent has been sulfur dioxide, hydrogen sulfide, thiosulfate, thionate, sulfonate 0r xanthate. In the absence of such addition agent, pure solutions such as those of manganese sulfate and ammonium sulfate, when electrolyzed, deposit manganese in the gamma or ductile form. This form of manganese cannot, however, be plated from pure solutions for periods of more than a few hours without a dropping off of current efficiency or even re-solution of the plate.

Practical electrowinning of manganese has been accomplished only by adding one or more of the sulfur-containing addition agents. The probable efiect of these addition agents is two-fold, viz: (1) they introduce sulfur in the electrolytic manganese and thereby bring about the deposition of the alpha or brittle form of manganese after a short period of plating, the sulfur acting as a catalyst for the transformation of gamma into alpha manganese, thus giving a duplex plate with a layer of gamma manganese against the cathode and the remainder of the plate, the alpha or brittle form. The deposition of the alpha form may be continued for a long period at high current efficiency; and (2) these addition agents maintain a reducing condition in the catholyte which prevents formation of insoluble manganese compounds. Other addition agents, such as hydroxylamine and aldehydes, have been found to fulfill the second requirement; but only sulfur compounds are known in the art to fulfill the first requirement.

It has been found that compounds containing no sulfur may be used to provide the catalyst for transforming gamma into alpha manganese during plating, if the compounds contain phosphorus or boron in the partially reduced state. Examples of such compounds are hypophosphites and hypoborites. ,Phosphites and various lower boric acid salts ofundetermined composition are also effective. The partially reduced boron compounds may be conveniently produced by adding boron hydrides particularly B4H10 to the usual manganese electrolyte. Hypophosphites, such as sodium hypophosphite, being readily available, are most conveniently used.- The amounts of these reagents used are not particularly critical; from .05 to .25 of a gram of sodium hypophosphite per liter of electrolyte has been found effective. Boron compounds may be present in an amount of the order of 0.1 gram per liter, computed as equivalent B4H1o.

By using the foregoing addition agents, the amount of sulfur in the manganese plate can be reduced to less than 0.03%, when using a sulfate electrolyte, without introducing more than 0.1% of either phosphorus or boron. The current efficiency, when 7 using these amounts of addition agents, will be as high as it is with the usual sulfur compound additions. These addition agents may be added to manganese electrolytes purified in any known manner; but they produce particularly good results when used with manganese solutions purified by adding sulfide ion according to the method of Ambrose, disclosed in U. S. Patent No. 2,347,451.

The sulfur content of electrolytic manganese, purified in accordance with the Ambrose method, may be lowered without loss of current efiiciency during plating by oxidizing the sulfide ion remaining in the filtrate after sulfide purification. In the preferred form of this method of preparing manganese solutions for electrolysis, sufiicient sulfide ion is added to the substantially pure solution to form a small amount of pink manganese sulfide at pH 7-8. Then the pH is adjusted, by adding ammonia or sulfuric acid, to 7-8 and the solution is held at this pH for about thirty minutes. It is then filtered and oxidized in accordance with this invention. This may be accomplished by agitating the solution in the presence of air until all of the sulfide ion has undergone the oxidizing reaction. This reaction naturally forms some colloidal sulfur, along with the desirable, partially-reduced sulfur compounds. The solution is, therefore, again filtered to remove the sulfur. Activated charcoa1 or other finely divided, inert, and adsorbent solid material may be employed to clarify the solution in the usual manner. The solution, so prepared, will be free from sulfide ion; but will have an iodine titration value equivalent to 1-3 milligrams of H25 per liter.

The treated solution may be used directly for the electrowinning of manganese in accordance with known procedures; but without any addition agent, such as S02, heretofore required to be added in the cell. The resulting manganese will contain .01-.03% sulfur. Since in usual practice, about 15 grams per liter of manganese is plated, it will be seen that the reduced sulfur compounds do not accumulate in the solution to any substantial extent. This is a great advantage over the known art in which sulfites or S02 are added and steps are taken to remove accumulated sulfur compounds. An example of such a step is the addition of ferrous sulfate and bubbling air through the solution. With the method of this invention, no such step is necessary.

While the sulfur introduced into the manganese by this method is sufficient to bring about the desired transition of the gamma manganese to alpha, during deposition, the current efficiency is not as high as when sulfites are added in the usual amounts of about .10 gram 802 per liter. However, the current efiiciency can be increased by adding partially reduced phosphorous or boron compounds. The amount of phosphorous or boron so introduced in the metal is negligible, always being less than .01% and these addition agents are not cumulative in a cyclic operation, because they are completely oxidized by Mn02. This, of course, is not true of sulfites which form thionates with M1102.

While this invention has been described in connection with the usual electrolyte of manganese and ammonium sulfates, it may also be used with chloride electrolytes or any other combination of manganese salts from which manganese can be plated. The invention has been described as applied to a substantially pure solution, but it will be obvious to those skilled in the art, that heavy metals present as impurities, will be removed incidental to the treatment with sulfide ion, as prescribed.

Since certain changes can be made without departing from the spirit and scope of this invention, it is intended that all matter set forth herein shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In the method of treating a manganeseammonium sulphate solution for electrolysis to produce a deposit of alpha manganese, wherein sulfide ion is added to remove traces of metallic impurities and the solution is filtered, the step of oxidizing the sulfide ion remaining in the solution after such filtration which comprises agitating the solution in the presence of air to the completion of the oxidizing reaction, and thereby converting all of the sulfide ion present into partially reduced sulfur compounds and colloidal sulfur; adding a finely divided, inert, adsorbent material to clarify the solution; filtering the clarified solution; and electrolysing said solution.

2. The method, asset forth in claim 1, further characterized by adding sodium hypophosphite in an amount between .05 and .25 of a gram per liter of the solution.

JOHN KOSTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,347,451 Ambrose Apr. 25, 1944 FOREIGN PATENTS Number Country Date 540,228 Great Britain Oct. 9, 1941 

1. IN THE METHOD OF TREATING A MANGANESEAMMONIUM SULPHATE SOLUTION FOR ELECTROLYSIS TO PRODUCE A DEPOSIT OF ALPHA MANGANESE, WHEREIN SULFIDE ION IS ADDED TO REMOVE TRACES OF METALLIC IMPURITIES AND THE SOLUTION IS FILTERED, THE STEP OF OXIDIZING THE SULFIDE ION REMAINING IN THE SOLUTION AFTER SUCH FILTRATION WHICH COMPRISES AGITATING THE SOLUTION IN THE PRESENCE OF AIR TO THE COMPLETION OF THE OXIDIZING REACTION, AND THEREBY CONVERTING ALL OF THE SULFIDE ION PRESENT INTO PARTIALLY REDUCED SULFUR COMPOUNDS AND COLLOIDAL SULFUR; ADDING A FINELY DIVIDED, INERT, ADSORBENT MATERIAL TO CLARIFY THE SOLUTION; FILTERING THE CLARIFIED SOLUTION; AND ELECTROLYSING SAID SOLUTION. 